GETPRIORITY(2) BSD System Calls Manual GETPRIORITY(2)
NAMEgetpriority, setpriority -- get/set program scheduling priority
SYNOPSIS#include<sys/resource.h>intgetpriority(intwhich, id_twho);
intsetpriority(intwhich, id_twho, intprio);
DESCRIPTION
The scheduling priority of the process, process group, or user as indicated by which and who is
obtained with the getpriority() call and set with the setpriority() call. Which is one of
PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, and who is interpreted relative to which (a process identifier
for PRIO_PROCESS, process group identifier for PRIO_PGRP, and a user ID for PRIO_USER). A zero value
of who denotes the current process, process group, or user. prio is a value in the range -20 to 20.
The default priority is 0; lower priorities cause more favorable scheduling.
The getpriority() call returns the highest priority (lowest numerical value) enjoyed by any of the
specified processes. The setpriority() call sets the priorities of all of the specified processes to
the specified value. Only the super-user may lower priorities.
Additionally, the current thread or process can be placed in a background state by specifying PRIO_DAR-WIN_THREAD PRIO_DARWIN_THREAD
WIN_THREAD or PRIO_DARWIN_PROCESS for which. Only a value of zero (the current thread or process) is
supported for who when setting or getting background state. prio is either 0 (to remove current thread
from background status) or PRIO_DARWIN_BG (to set current thread into background state). When a thread
or process is in a background state the scheduling priority is set to the lowest value, disk IO is
throttled (with behavior similar to using setiopolicy_np(3) to set a throttleable policy), and network
IO is throttled for any sockets opened after going into background state. Any previously opened sock-ets sockets
ets are not affected. The getpriority() call returns 0 when current thread or process is not in back-ground background
ground state or 1 when the current thread is in background state. Any thread or process can set itself
into background state.
RETURNVALUES
Since getpriority() can legitimately return the value -1, it is necessary to clear the external vari-able variable
able errno prior to the call, then check it afterward to determine if a -1 is an error or a legitimate
value. The setpriority() call returns 0 if there is no error, or -1 if there is.
ERRORSGetpriority() and setpriority() will fail if:
[EINVAL] Which is not one of PRIO_PROCESS, PRIO_PGRP, PRIO_USER, PRIO_DARWIN_THREAD, or
PRIO_DARWIN_PROCESS.
[EINVAL] Who is not a valid process, process group, or user ID.
[EINVAL] Who is not 0 when which is PRIO_DARWIN_THREAD or PRIO_DARWIN_PROCESS.
[ESRCH] No process can be located using the which and who values specified.
In addition to the errors indicated above, setpriority() will fail if:
[EACCES] A non super-user attempts to lower a process priority.
[EPERM] A process is located, but neither its effective nor real user ID matches the effec-tive effective
tive user ID of the caller.
LEGACYSYNOPSIS#include<sys/types.h>#include<sys/resource.h>
The include file <sys/types.h> is necessary.
intgetpriority(intwhich, intwho);
intsetpriority(intwhich, intwho, intvalue);
The type of who has changed.
SEEALSOnice(1), fork(2), setiopolicy_np(3), compat(5), renice(8)HISTORY
The getpriority() function call appeared in 4.2BSD.
4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution

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